patch 8.1.2000: plugin cannot get the current IME status

Problem:    Plugin cannot get the current IME status.
Solution:   Add the getimstatus() function. (closes #4904)
diff --git a/src/proto/mbyte.pro b/src/proto/mbyte.pro
index b9f0439..86b525c 100644
--- a/src/proto/mbyte.pro
+++ b/src/proto/mbyte.pro
@@ -90,6 +90,7 @@
 int im_is_preediting(void);
 void xim_set_status_area(void);
 int xim_get_status_area_height(void);
+void f_getimstatus(typval_T *argvars, typval_T *rettv);
 int convert_setup(vimconv_T *vcp, char_u *from, char_u *to);
 int convert_setup_ext(vimconv_T *vcp, char_u *from, int from_unicode_is_utf8, char_u *to, int to_unicode_is_utf8);
 int convert_input(char_u *ptr, int len, int maxlen);